CVE-2024-40909

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix a potential use-after-free in bpf_link_free()

After commit 1a80dbcb2dba, bpf_link can be freed by

link->ops->dealloc_deferred, but the code still tests and uses

link->ops->dealloc afterward, which leads to a use-after-free as

reported by syzbot. Actually, one of them should be sufficient, so

just call one of them instead of both. Also add a WARN_ON() in case

of any problematic implementation.